Electromagnetically driven vibrators are usually operated at the same frequency or double the frequency of the alternating current power supplied to the electromagnet constituting the feeder motor. Since most power systems operate at 60 Hz. or 50 Hz. the feeders operate at frequencies of 3000, 3600, 6000 or 7200 cycles per minute.
These frequencies are too high for good vibratory conveying, and the limitation of operation to precisely the stated frequencies requires that much of the electromagnetically generated force be used to synchronize the mechanical vibration to the operating frequency leaving only a small portion to do useful work. These feeders if tuned close to the operating frequency were very sensitive to changes in load, either overstroking at light or no load and stalling with increases in load over the design load.